Justin Trudeau became Canada’s 23rd Prime Minister as the Liberal Party seized a decisive 184-seat majority in the 338-seat parliament. The Conservatives came second with 99 seats, the NDP was booted from opposition to third place with 44, the Bloc Quebecois took 10 and Elizabeth May held onto the Green Party’s only seat.

“The disappointment you also feel is my responsibility and mine alone,” Harper said during his late-night concession speech from his riding of Calgary-Heritage. “While tonight’s result is certainly not the one we had hoped for, the people are never wrong,”

Mention of Harper’s resignation was conspicuously absent from the former leader’s speech. Conservative Party President John Walsh released a statement ahead of Harper taking the stage, saying the party had been instructed to start the process to select an interim leader and the leadership selection process.

“Stephen Harper was such a dominant figure as a Prime Minister and leader of the Conservative party; the one who helped unify the party and won several elections in a row,” said Daniel Béland, Research Chair in Public Policy for Johnson-Shoyama Graduate School of Public Policy at the University of Saskatchewan. “I think relatively few people in the party, even former ministers, have this image that is strong enough to really lead them to run and to have a chance to actually have a shot at being Prime Minister.”

Harper has been the only leader of the new Conservative Party that formed from the merger of the socially conservative Canadian Alliance and socially centrist Progressive Conservative parties in 2003. As the former leader of the Canadian Alliance, Harper was vital to brokering the merger deal.

Béland said Harper walked the tightrope over the Alliance/Progressive divide that still exists within the party and commanded a strong party whip. He said the ability to keep the party united will be the greatest challenge and asset to potential leadership candidates.

It comes with opportunities for the party to renew itself but it also comes with great risk of exacerbating internal tensions,” Béland said. “Some people are interested in having a real debate in the (Conservative) party because they were muzzled for a long time in the name of securing and maintaining the party in power.”

While Béland said it’s still unclear if the next leader could command the party as Harper did, he conceded that Canadians have yet to get to know many other Conservative members, due to Harper’s all-present concentration of power and messaging.

“People may not seem that strong at first but then during a leadership race we can discover personalities,” he said.

The four assets Béland said the future leader must demonstrate are charisma to combat Trudeau’s popularity, support from both sides of the party, a more moderate approach to appeal to a wider Canadian voter base, and the ability to win over women and minority voters.

List of potential candidates

Jason Kenney

Kenney served as Harper’s minister of national defence and minister of multiculturalism where he helped push gains in the nation’s ethnically diverse ridings. A former Reform member, Kenney served as MP for Calgary Southeast since 1997 and seized a decisive victory Monday in the newly redrawn riding of Calgary Midnapore.

Kenney is popular among the party’s western base and considered a favourite to replace Harper, but Béland said his social conservatism may be a “liability in gaining ground in the east.”

Lisa Raitt

Raitt took the reigns as Harper’s transportation minister in 2013 following her previous positions of Minister of Labour and Minister of Natural Resources. She was re-elected in the Milton, Ont. riding she’s held since 2008.

Raitt may be considered a potential future Conservative leader because of her more socially centrist views, Béland said, allowing her to appeal to a wider voter audience. However, it’s unclear if Harper’s crafted social conservative party image would accept a Red Tory at the helm.

Peter MacKay

In May, the former justice minister announced he would not see re-election following two decades of federal politics in order to focus on his young family.

MacKay was the last leader of the Progressive Conservative party before the merger with the Reform Party.

Béland said like Raitt, MacKay’s Progressive roots and social centrist leanings may prove an asset in combating the Liberal’s centrist way of governing.

Jean Charest

Before his retirement as leader of the Quebec Liberal Party in 2012, nine years of which he spent as Premier of Quebec, Charest became leader of the federal Progressive Conservative Party in 1993. He remained at the head for five years until Quebec federalism called him back to the politics of his native province.

Charest left politics three years ago and it’s unclear if he would return to seek the nomination.

Brad Wall

Considered Canada’s most popular premier, Wall’s two consecutive Saskatchewan Party majorities have placed him in a unique position to jump to federal politics. His positions on senate abolition and reconsidering equalization payments have made him a popular prairie leader who has also shown an ability to balance true blue and red Tories to unify a party and win votes.

On Tuesday Wall said he would not seek the top Conservative spot, has ruled out seeking any federal position and will instead “reapply” for a third term as premier in the province’s April 2016 election.

“No, I have this great job. I’m humbled to have it,” Wall said when asked if he would run federally.

Other potential candidates

Tony Clement, candidate for the leadership of the Conservative Party after its formation, Minister of Health and most recently president of the Treasury Board before the election

Maxime Bernier, minister of industry, minister of foreign affairs and most recently minister of small business before the election

James Moore, Minister of Canadian Heritage and Official Languages. Was minister of industry before the election and did not seek reelection.

Pierre Poilievre, employment minister before the election.

Bernard Lord, former New Brunswick premier.

Doug Ford, former Toronto city councillor and brother to former Mayor Rob Ford.